[LTO] Include debug options in legacy ThinLTO cache keys (#211474)

Legacy ThinLTO omits -mllvm options from cache keys, which can cause it
to reuse objects built with different code-generation settings.

Include these options in cache keys, matching modern ThinLTO behavior.

llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h

@@ -236,6 +236,11 @@ public:
   /// Enable or disable debug output for the new pass manager.
   void setDebugPassManager(unsigned Enabled) { DebugPassManager = Enabled; }
 
+  /// Set the -mllvm arguments to include in the cache key.
+  void setMllvmArgs(ArrayRef<std::string> Args) {
+    MllvmArgs.assign(Args.begin(), Args.end());
+  }
+
   /// Disable CodeGen, only run the stages till codegen and stop. The output
   /// will be bitcode.
   void disableCodeGen(bool Disable) { DisableCodeGen = Disable; }
@@ -356,6 +361,9 @@ private:
   /// Flag to indicate whether debug output should be enabled for the new pass
   /// manager.
   bool DebugPassManager = false;
+
+  /// -mllvm arguments included in the cache key.
+  std::vector<std::string> MllvmArgs;
 };
 }
 #endif

llvm/lib/LTO/ThinLTOCodeGenerator.cpp

@@ -379,7 +379,8 @@ public:
       const FunctionImporter::ExportSetTy &ExportList,
       const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
       const GVSummaryMapTy &DefinedGVSummaries, unsigned OptLevel,
-      bool Freestanding, const TargetMachineBuilder &TMBuilder) {
+      bool Freestanding, const TargetMachineBuilder &TMBuilder,
+      ArrayRef<std::string> MllvmArgs) {
     if (CachePath.empty())
       return;
 
@@ -400,6 +401,7 @@ public:
     Conf.RelocModel = TMBuilder.RelocModel;
     Conf.CGOptLevel = TMBuilder.CGOptLevel;
     Conf.Freestanding = Freestanding;
+    append_range(Conf.MllvmArgs, MllvmArgs);
     std::string Key =
         computeLTOCacheKey(Conf, Index, ModuleID, ImportList, ExportList,
                            ResolvedODR, DefinedGVSummaries);
@@ -1152,7 +1154,7 @@ void ThinLTOCodeGenerator::run() {
                                     ImportLists[ModuleIdentifier], ExportList,
                                     ResolvedODR[ModuleIdentifier],
                                     DefinedGVSummaries, OptLevel, Freestanding,
-                                    TMBuilder);
+                                    TMBuilder, MllvmArgs);
         auto CacheEntryPath = CacheEntry.getEntryPath();
 
         {

llvm/test/tools/lto/legacy-thinlto-cache-key.ll

@@ -0,0 +1,43 @@
+; Verify that legacy ThinLTO includes -mllvm arguments in its cache keys.
+; Cache an unoutlined object, enable outlining, then reuse the first
+; configuration. The products and cache-entry count must match each option set.
+; RUN: opt -module-summary -module-hash %s -o %t.o
+; RUN: rm -rf %t.cache && mkdir %t.cache
+
+; Populate the cache with an unoutlined object.
+; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -arch x86_64 -macosx_version_min 10.8.0 -dylib -cache_path_lto %t.cache -o %t.not-outlined.dylib %t.o -lSystem
+; RUN: llvm-nm --no-llvm-bc %t.not-outlined.dylib | FileCheck --check-prefix=NO-OUTLINED %s
+; RUN: ls %t.cache/llvmcache-* | count 1
+
+; Enabling the outliner must miss the existing entry and create a distinct one.
+; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -arch x86_64 -macosx_version_min 10.8.0 -dylib -cache_path_lto %t.cache -o %t.outlined.dylib %t.o -lSystem -mllvm -enable-machine-outliner
+; RUN: llvm-nm --no-llvm-bc %t.outlined.dylib | FileCheck --check-prefix=OUTLINED %s
+; RUN: ls %t.cache/llvmcache-* | count 2
+
+; Omitting the option again must reuse the unoutlined cache entry.
+; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -arch x86_64 -macosx_version_min 10.8.0 -dylib -cache_path_lto %t.cache -o %t.not-outlined.dylib %t.o -lSystem
+; RUN: llvm-nm --no-llvm-bc %t.not-outlined.dylib | FileCheck --check-prefix=NO-OUTLINED %s
+; RUN: ls %t.cache/llvmcache-* | count 2
+
+; OUTLINED: OUTLINED_FUNCTION_
+; NO-OUTLINED-NOT: OUTLINED_FUNCTION_
+
+target triple = "x86_64-apple-macosx10.8.0"
+
+define void @outline_me() #0 {
+  %slot = alloca i32, align 4
+
+  ; Two copies form a profitable outlining candidate.
+  store i32 1, ptr %slot, align 4
+  store i32 2, ptr %slot, align 4
+  store i32 3, ptr %slot, align 4
+  store i32 4, ptr %slot, align 4
+  store i32 1, ptr %slot, align 4
+  store i32 2, ptr %slot, align 4
+  store i32 3, ptr %slot, align 4
+  store i32 4, ptr %slot, align 4
+  ret void
+}
+
+; Preserve the stores and make outlining profitable.
+attributes #0 = { noinline optnone noredzone "frame-pointer"="all" }

llvm/tools/lto/lto.cpp

@@ -95,6 +95,9 @@ static enum class OptParsingState {
 
 static LLVMContext *LTOContext = nullptr;
 
+// Records -mllvm arguments parsed through the legacy debug-option APIs.
+static std::vector<std::string> ThinLTOMllvmArgs;
+
 struct LTOToolDiagnosticHandler : public DiagnosticHandler {
   bool handleDiagnostics(const DiagnosticInfo &DI) override {
     if (DI.getSeverity() != DS_Error) {
@@ -554,6 +557,7 @@ lto_bool_t lto_module_has_ctor_dtor(lto_module_t mod) {
 thinlto_code_gen_t thinlto_create_codegen(void) {
   lto_initialize();
   ThinLTOCodeGenerator *CodeGen = new ThinLTOCodeGenerator();
+  CodeGen->setMllvmArgs(ThinLTOMllvmArgs);
   CodeGen->setTargetOptions(
       codegen::InitTargetOptionsFromCodeGenFlags(Triple()));
   CodeGen->setFreestanding(EnableFreestanding);
@@ -630,11 +634,12 @@ void thinlto_codegen_set_codegen_only(thinlto_code_gen_t cg,
 }
 
 void thinlto_debug_options(const char *const *options, int number) {
-  // if options were requested, set them
+  // If options were requested, parse and retain them.
   if (number && options) {
     std::vector<const char *> CodegenArgv(1, "libLTO");
     append_range(CodegenArgv, ArrayRef<const char *>(options, number));
     cl::ParseCommandLineOptions(CodegenArgv.size(), CodegenArgv.data());
+    ThinLTOMllvmArgs.assign(options, options + number);
   }
 }